James Allen is being urgently sought by police following the separate murders of Julie Davison, 50, in Whitby, North Yorkshire, and 81-year-old Colin Dunford in Middlesbrough.

Allen, 35, has previous convictions for violence and has served a custodial sentence, Detective Chief Superintendent Gordon Lang told a press conference in Middlesbrough yesterday.

On Saturday, Lang said sightings of Allen in the Cleveland and North Yorkshire Police areas were continuing to be reported as well as potential sightings in Leeds on Thursday and Friday.

The detective said it was possible that Allen was trying to change his appearance by growing his hair.

Lang said: "We are investigating a number of sightings in both force areas that have been reported to us, including sightings in the Harehills area of Leeds, and I would repeat our message in urging members of the public if you see James Allen to call 999 immediately.

"This operation continues on a 24/7 basis and it will do until we trace and arrest James Allen."

Mr Lang urged anyone who knows where Allen is to contact police.

"Someone must know where he is. He will have confided in someone and I would appeal to that person to come forward and get in touch with us," he said.

Murder victims Julie Davison and Colin Dunford

"Two innocent people have lost their lives and it is absolutely vital that we catch James Allen as soon as possible.

"If you know where he is now, call us. James, if you are reading this, give yourself up, it is only a matter of time before we find you."

Allen is believed to have stayed at the Allerton Croft hotel, in Scarborough, on Wednesday evening, following Ms Davison's death.

Drinkers at the Lord Rosebery pub in the seaside town also reported seeing someone fitting Allen's description.

A spokesman for the Wetherspoon's branch said police had been informed of the sighting and members of the regional crime squad would be viewing CCTV footage.

On Friday, Lang confirmed that Allen was on court bail for an offence, although he did not disclose what it was.

He also said Allen had had contact with the probation services and was being investigated for other alleged offences, which he would also not disclose.

Lang warned residents to keep their homes secure and be careful when answering their doors.

He added: "Clearly this is a man who is a dangerous man, but we are putting absolutely everything into finding him, tracking him down and bringing him to justice.

"There's a massive police operation in place here. Over 100 detectives, two forces, not an inch between these two forces, absolutely working in partnership with one goal, and that is to find James Allen and arrest him.

"We are 100% committed to tracking him down."

Lang said Allen, originally from Blackpool, knew Dunford when he lived next door to him in Leven Street about a year ago but it is not thought Allen knew Davison.

He said robbery was a possible motive behind the attacks, but stressed he was keeping an open mind.

The senior detective said the suspect could have tricked his way into Davison's home.

Officers are keen to trace a black bicycle with suspension which Allen had with him.

Lang said it was feasible that Allen had cycled between Middlesbrough and Whitby - a distance of more than 30 miles (48km) - although the officer said they were also looking at other modes of transport he may have used.

Cleveland Police and North Yorkshire Police issued a joint appeal to find Allen after officers linked the two deaths on Thursday.

A post-mortem examination on Dunford, who was last seen alive at around 5pm last Sunday, showed he had suffered serious head injuries.

He was found dead at his terrace house in Leven Street, Middlesbrough, on Monday after he failed to appear at Samuelsons Working Man's Club, where he was a daily visitor.

Detectives said there was no sign of forced entry at the house.

Davison, who lived alone, was found dead by her sister at her rented flat in Church Square on Wednesday. She had also suffered serious head injuries, police said.

Police described the killings as "two brutal murders in the victims' own homes".